> The product is just too complicated (tons of domain knowledge required) for someone to come in and take over.
I doubt that this is actually true. It may take them time to ramp up, but you're there to guide them and mentor them.
> Additionally, the product just isn't that interesting (glorified CRUD app) and it's been hard to retain developers.
The fact that you're deeply involved and don't feel that other developers can step in, and at the same time feel like it's a glorified CRUD app hints that you may not be giving other developers enough autonomy or context on the problem.
If they are just working on simple CRUD stuff and have no context, the job is going to suck. But simple CRUD with context could be much more interesting.
And if all else fails, pay more.